1. Technical Field
The present invention relates to a coaxial valve comprising a valve housing, on which an inlet port and at least one outlet port for a medium which is to be conducted through the coaxial valve are provided, a control tube which is mounted in the valve housing, said control tube being movable in its longitudinal direction in the valve housing and interacting with the inlet port and the outlet port in such a way that when the coaxial valve is opened medium flows through the control tube, at least one valve seat having a valve seat face, the control tube interacting with the valve seat face in one of its axial end positions in order to close the coaxial valve, and a control device for moving the control tube between its axial end positions.
2. Background Art
Such a co-axial valve is known, for example, from DE 101 08 492 A1.
The known coaxial valves are used to regulate and shut off fluid or gaseous media, wherein these media may be chemically aggressive and may be present at high or low temperatures as well as at high pressures. Against this background, coaxial valves of this kind are subject to stringent requirements in terms of their tightness, mechanical reliability and service-friendliness.
Coaxial valves are used, for example, to supply machine tools with cooling lubricants which are made available by feeding them in at high pressures.
In these applications, the coaxial valves mentioned at the outset are used because they are completely relieved of pressure and the prevailing pressure of the medium to be transported therefore does not have any effect on the switching behaviour. In addition, the medium to be controlled flows through the coaxial valve without appreciable deflection of the flow in the axial direction, wherein the resistance of the coaxial valve to the flowing medium is very low.
Such coaxial valves have a control tube which is mounted in an axially movable fashion in a valve housing and through which the medium to be transported flows. The control tube interacts with a valve seat face on which the control tube rests in one of its axial end positions in such a way that the coaxial valve is closed.
In its opposed axial end position, the control tube is spaced apart from the valve seat face, with the result that the medium can flow freely through the coaxial valve.
As a rule, in coaxial valves of this type a valve spring is provided which prestresses the control tube into the opened position when the coaxial valves are of the type “open in the state of rest (NO=normally open)”, and correspondingly into the closed position when the coaxial valves are of the type “closed in the state of rest (NC=normally closed)”.
The movement of the control tube between the two end positions is carried out, for example, by means of an electromagnet which, when energized, acts on the control tube connected to an armature in such a way that said control tube is moved from its one coaxial end position into the other coaxial end position.
In addition to these directly controlled coaxial valves, externally controlled coaxial valves are also known in which the control valve acts as a piston rod which is connected to a piston which is activated via a control medium which is different from the medium to be switched. This control medium may be, for example, compressed air or hydraulic oil.
The control of the coaxial valves can be double-acting, with the result that the control tube is moved actively both into its closed position and into its open position. In the case of an externally controlled coaxial valve this means that the external medium can be applied to the piston on both of its sides. One of these movements can be assisted by the valve spring, although it is also known to construct coaxial valves without any valve spring.
Coaxial valves are as a rule available as 2/2-way valves or as 3/2-way valves that is to say with two or three external ports, but always with two operating positions.
The coaxial valve which is known from DE 101 08 492 A1 is a 3/2-way valve in which a valve seat with a valve seat face is provided at both ends of the control tube.
DE 10 2006 010 087 B4 discloses a 2/2-way valve in which the valve seat has a solid sphere which is secured in a press fit on a housing upper part of the valve housing. The solid sphere may be taken off together with the entire housing upper part.
All the coaxial valves described thus far have in common the fact that a front-side end of the sleeve-shaped control tube forms an annular face which rests on the valve seat face in the closed state of the coaxial valve.
The valve seat itself is provided with breakthroughs or surrounding openings or spaces through which the medium which flows out of the control tube passes to the outlet port in the opened state of the valve.
DE 101 08 492 A1 discloses that the valve seat face is not embodied as a planar face but rather as a cone envelope surface or a spherical surface.
Owing to the loading conditions during use, it can be observed again and again that dirt collects on the valve seat and both prevents secure closing of the valve and adversely affects the free flow of the medium through the opened valve.
For this purpose, known coaxial valves can be disassembled in order to be able to take off the valve seat and clean it.
In the coaxial valves described thus far, it is possible, for this purpose, to release part of the valve housing in the longitudinal direction of the control tube, that is to say in the direction of the flow of fluid, and to take it off, after which the valve seat face can then be cleaned, or the valve seat in its entirety can be replaced.
It has now become apparent that owing to the geometric conditions this axial removal of the valve seat is frequently problematic. Before disassembly of the valve housing becomes possible, the valve housing itself often must firstly be removed from the machine on which it is mounted.
However, the cleaning of the valve seat faces which is then possible sometimes does not lead to the desired success, with the result that the valve seat in its entirety has to be replaced. For this purpose, the valve seat has to be unscrewed from the housing part previously removed from the valve housing, and a new valve seat has to be screwed on, after which the housing part is then screwed onto the valve housing again, and said valve housing has to be mounted again on the machine which is controlled via the coaxial valve.
These measures overall are time-consuming, with the result that the downtimes which they entail for the controlled machines constitute, together with the cost of the replacement parts, a considerable cost burden.